Alloy steel



Patented Feb. 26, 1946 i ALLOY STEEL- Luciano o. Selmi, Detroit, and01mm L. Altenburger,'Deai-born, Mich. assignors to National SteelCorporation, a corporation of Delaware No Drawing. Application September30, 1942.

Serial No. 460,273

2- Claims. .(Cl. Fit-'12s) This invention relates to improvementsin lowalloy steels. More particularly, the invention relates to steels of thetype disclosed and claimed in applicants Patent No. 2,250,505 issuedJuly 29, 1941.

In the steels described in the foregoing patent. zirconium isincorporated as a constituent to deoxidize the steel and attain aninherently fine grain. In the present invention, by substitutingvanadium for the zirconium in similar steels the many advantages of thesteels of the patent have been retained while eliminating certaindisadvantages inherent in the use of zirconium. These disadvantagesinthe use of zirconium in no way affect the characteristics of thepatented steels but appear only during the manufacture. By the presentinvention a similar steel incorporating the same characteristics asthose of the patented steels can be more easily produced, thesubstitution of vanadium for the zirconium eliminating many of thepouring and casting troubles encountered with the use of zirconium. Onthe render a steel of this general nature highly re- I treatment.

other hand we have found that the incorporation of the vanadium in placeof the zirconium does not deleteriously affect the physicalcharacteristics of the specific steel-involved. Thus the steel of thepresent invention has substantially the same physical characteristics asthe, steels disclosed in Patent No. 2,250,505.

The general object of the present invention is to provide a steel whichmay be easily and economically manufactured and which shall haveimportant characteristics heretofore obtained only in steels usinglarger quantities of alloying metals.

More specifically, steels heretofore manufactured which have theproperties of high degree Steels now on the market havingcharacteristics and properties such as are attained by our presentinvention, include alloying metals in substantially highpercentages-such for example as follows:

Nickel 1.75 Molybdenum .35 Chromium .75 Carbon .40 Manganese .70 Siliconv .20 Phosphorus, maximum .03 Sulphur, maximum .03 Aluminum lb. per ton1 It will be seen that in the foregoing example of commercial steelcomparatively high percentages of these variable alloying elements havebeen heretofore considered essential to attain certain characteristics.We attainthe essential characteristics of such a steel as willhereinafter appear or high levels of hardness, variable hardenability,

' purposes.

Further pecific objects therefore are to obtainin an alloy steel certainherein described characteristics with the use of a low percentage ofalloy elements.

Further specific objects include the provision of a steel which shall beresistant to a very high velocity impact. resistant to shock andfragmentation, and which shall have permanent high cohesive strength. Itis desirable that the steel of the present invention shall have thishigh cohesive strength with a high ratio of such cohesive strength toits shear strength. Thus the steel is resistant to growth of andpropagation of cracks.

Another object 'of thepresent invention is to with comparatively lowpercentages of such alloying elements as nickel and thus effect markedeconomies.

With the low alloy metals of the percentages such as herein given, weare enabled to provide a steel having an inherently fine grain and inwhich hardenability may be varied as desired through heretoforeunexpectedly wide ranges by relatively small variations in the elements.[Likee wise we are able to provide a steel in which the hardenabilitymay be varied by small changes of the quenching temperatures.

All of the above purposes and characteristics are attained within rangesof very much. lower cost per ton.

Furthermore. we are enabled to maintain uniformity of product heretoforediflicult to obtain with anything comparable to our small percentages ofthe alloying elements.

Steels according to the present invention will.

have compositions within the following ranges:

Below is given-a specific example of a steel similar to the steel of thepresent invention to from the 2 which no molybdenum has been added andan. example of the steels oi the present invention:

SteslA Swan Trace .14

Steel A has a hardness in excess of 50 Rockwell 0, along a net endquench bar up to 1 inch quenching end when quenched from 1500'1'. v

Steel B has a hardness in excess of 50 Rockwell along 2 inches or morefrom the, quenched end when quenched from 1500' l".

In these examples, both steels are held at 1500" l". for one hour priorto quenching. Both are one inch round bars.

Steel A. must be cooled at a rate in excess of 21' F. per second at1250' r. to harden above so Rockwell C, whereas in the example given forthe steel B,- cooling may be as slow as about 23 I. per second throughthe temperature or 1250 F.

and still it will harden above the level of 50 Rockwell C.

From the, foregoing examples, it will be noted that the marked increaseddepth of hardenability or the steel B over the steel A accompanies theincrease of molybdenum. In the Example A, the molybdenum given is but atrace. In the ExampleB, molybdenum is given at 0.14%. Varying this rangeor molybdenum, while still maintaining it in within comparatively smallquantity range, we have found our steels are hardenable through greatdepths, and it is entirely practical within the range, say. of up to0.35% molybdenum to harden locomotive or car axles throughout.

that is, through thicknesses of six inches or more.

It willalso be noted that the relative hardenability between our steelsA and B is accompanied with but slight changes in the other alloyingelemanta which are all maintained within comparative low percentages.The carbon in Example B is slightly less than Example A; the manganeseis slightly higher; the silicon is raised in the Example B from .75 to39%; chromium is preferably slightly increased; the molybdenum shows themarked change, being raised from a trac up too. substantial, but stilllow amount. I

As will be seen from the example given of a steel heretotoreused inwhich a comparatively highpercentage oi a notably expensive element,such as nickel is used, such higher percentage, namely 1.75% seems tohave been heretofore'considered essential to attain the characteristicswhich we attain.

In particular reference to hardenability, widely assess? ature, withshapes having comparatively thin or narrow crow-sections. The steel Amay thus Practically be treated to attain desired hardness levelsthroughout by variations of quenching tem-' I v peraturesthrough narrowranges.

Examples of the eiiects obtained by variati in cooling rates andquenching temperatures in the treating or steelB are tabulated below asillustrative. From these tables the increased hardenability eilected bychange in temperature and the resulting levels .01 hai-dness' which wehave found are clearly apparent.

The left-hand column lists the dii'lerences from the quenched end of thedepth or distance to which the hardness reaches. The second column 1gives the cooling rate passing through the temperature oi 1250 F. Thethird and fourth columns list Rockwell C hardness when quenched, usingtemperatures 01' 1475 F. and 1500 F., and after seventy-five minutes. 7

Steel B, in which more molybdenum is used, a

as for instance in the example given, is likewise responsive to slightchanges in, th quench temperature but its hardenability throughout isgoverned more by the presence oi molybdenum.

Examples of uses of alloy steels made in accord-,

ance with our present invention and which may be furnished at low costcompared to present alloys used for like purposes are: automobile axles,

gears, automobile springs, airplane propellers,

airplane engine shafts and many other parts where exceptionally deephardening is required such as, for example, large axles for railwayuses.

The expense or cost or the alloys for steels now used for agiven weightor part may be several 7 times that of steels made in accordance withour used steels such as having the first-given formula,

may have their quality of hardness varied only comparatively slightly bywidely varying th quenching temperatures.

With our present steel we may vary the levels or hardness through markedranges by slight variations in temperatures.

Steels, such as the example given, and others heretofore used, requirevariations in quenching temperatures of as high as 200 1''. forcorresponding results.

A steel such as steel A may have its degree or levels of hardness variedmaterially by changes of as little as 20 degrees in quenchingtemperpresent invention and having like or in some respects superiorcharacteristics.

By the present invention, we have produced, as aboveindicated, aninherently fine grained, clean steel. It is substantially deoxidized andit is sub- Ject to controlling the degree and depth 01- its hardness.

A steel, such as Example B, above-described, is highly resistant toquench cracking. It will withstand a drastic quench treatment such asthat of live percent caustic solution from above critical temperatures;for example, 1480" F. down to 32: F.

The steel has a balanced alloy composition and the relationship betweenthe molybdenum. when used, and the other elements, have surprisinglycritical characteristics accomplishing the objects as above set forth.

The oxidizing elements present in the steel are such as to produce lowdegrees of distortion during high heat treatment. The steel, unlikeother steels having comparable degrees of hardenability, has inherentproperties which result in a steel suitable for convenient and practicalfabrication such as forging and otherwise working. Our present steel hascharacteristics of weldability that compare with alloys having likepropertiesbut which, as. heretofore indicated, must have higherpercentages of other elements, such, for example,

as nickel. v

. ,We' have found that in using the steel of the certain optimumpercentages of the constituents exist inaccordance with the. thicknessor the plate. The following table shows some of these preferredcompositions:

Pietethinlmmininehes I Upto 1 2andup 0.3-0.8!) are-ea amen .50- .15 .85-.co-un .50- .90 .50- .90 .m- .00 .50 .75 .00 .eo- .lo- .20 .10- .10-.01- .10 .01- .Ql- JO present invention 'for heat treated plates that Weclaim:

1. A low alloy steel having inherently fine grain with hardenabilityvariable through wide ranges, consisting of carbon .26 to 310%;manganese .74 to 1.00%; silicon .50 to- .90%; chromium .50 to 115%;molybdenum .05- to 25%; vanadium .01 to .l.0%; the balance being ironand incidental imp s- I 2. A low alloy steel having inherently flnegrain with hardenability variable through wide ranges, consisting ofcarbon .26 to 50%; manganese .85

,to 1.00%;silicon .50 to .90%; chromium .60 to 310%: molybdenum .10 to20%; vanadium .01 to 10%: the balance being iron and incidentalimpurities. v

- LUCIANO G. SELMI. v CLARENCE L. ALTENBURGER.

